1. Technical Field
The present invention relates to a food weight detecting device for a microwave oven, and more particularly to a food weight detecting device for a turntable-rotation type microwave oven which can detect food weight accurately according to variations in the angular velocity of the turntable.
2. Prior Art
FIG. 1 shows a conventional food weight detecting device for a microwave oven. The device comprises a synchro motor 1 for providing a rotating force when electric power is supplied, a rotating shaft 2 that rotates a turntable by means of the provided rotating force and moving upward or downward according to the weight of food on the turntable, a weight sensing section 5, having an upper plate 3 and a lower plate 4 facing each other, for sensing the variation of capacitance value as weight information according to the variation of the interval between the upper plate 3 and the lower plate 4 due to upward or downward movement of the rotating shaft 2, an LC oscillating section 6 for generating a frequency signal which varies corresponding to the varied capacitance value, a buffer section 7 for shaping the generated frequency signal to a rectangular wave, and a microcomputer 8 for receiving the shaped rectangular wave and evaluating the weight of food on the turntable according to the frequency of the rectangular wave.
The conventional device having the above-described construction is operated as follows. First, if a user applies electric power to the microwave oven to heat food, the rotating shaft 2 is rotated by the synchro motor 1 and the turntable mounted on the rotating shaft 2 is rotated. In this case, the rotating shaft 2 moves upward or downward according to the weight of food being heated on the turntable, so that the weight sensing section 5 senses the weight of food on the turntable.
That is, if the upper plate 3, having an appropriate elastic force, is forced by the upward or downward movement of the rotating shaft 2, the interval between the upper plate 3 and the lower plate 4 will vary according to the upward or downward movement of the upper plate 3, thereby the capacitance value provided from the weight sensing section 5 composed of the upper plate 3 and the lower plate 4 will also vary. The varied capacitance value is supplied to the LC oscillating section 6 and an oscillating frequency signal, which varies according to the variation of the capacitance value, is outputted from the LC oscillating section 6. The outputted frequency signal is shaped to a rectangular wave by the buffer 7 and then is supplied to the microcomputer 8, so that the microcomputer 8 evaluates the weight of food on the turntable according to the frequency of the rectangular wave.
However, in the above-mentioned food weight detecting device, physical deformation is apt to be produced by defects such as the scale and/or the secular change of the material quality of the upper plate 3 and the lower plate 4, thereby there is a great possibility that the precise change of the capacitance value may not be detected.
Further, there are several disadvantages that the synchro motor 1 must be disposed at the center portion under the turntable since the rotating shaft 2 is disposed at the center portion of the turntable, and that microwaves will leak through the rotating shaft penetrating pore formed at the lower part of a heating cavity.